Abstract: A gas turbine engine comprises a fan, a core turbine engine coupled to the fan, a fan case housing the fan and the core turbine engine, a plurality of outlet guide vanes extending between the core turbine engine and the fan case, and an acoustic spacing. The fan comprises a plurality of fan blades that define a fan diameter and a BEAL. The fan case comprises an inlet and an inlet length between the inlet and the fan. The acoustic spacing comprises a distance between the fan and the plurality of outlet guide vanes, and in combination with the BEAL determines an acoustic spacing ratio of the gas turbine engine.

Abstract: An aircraft engine includes a low pressure spool, a high pressure spool, and an alternative power source. The alternative power source is configured to add power to the high pressure spool. A controller is configured to determine a noise sensitive condition; and control, in response to determining the noise sensitive condition, the alternative power source to add power to the high pressure spool.

Abstract: A heat exchanger positioned within an annular duct of a gas turbine engine is provided. The heat exchanger extends substantially continuously along the circumferential direction and defining a heat exchanger height equal to at least 10% of a duct height. An effective transmission loss (ETL) for the heat exchanger positioned within the annular duct is between 5 decibels and 1 decibels for an operating condition of the gas turbine engine. The heat exchanger includes a heat transfer section defining an acoustic length (Li), and wherein an Operational Acoustic Reduction Ratio (OARR) is greater than or equal to 0.75 to achieve the ETL at the operating condition.

Abstract: A heat exchanger positioned within an annular duct of a gas turbine engine is provided. The heat exchanger extends substantially continuously along the circumferential direction and defining a heat exchanger height equal to at least 10% of a duct height. An effective transmission loss (ETL) for the heat exchanger positioned within the annular duct is between 5 decibels and 1 decibels for an operating condition of the gas turbine engine. The heat exchanger includes a heat transfer section defining an acoustic length (Li), and wherein an Operational Acoustic Reduction Ratio (OARR) is greater than or equal to 0.75 to achieve the ETL at the operating condition.

Abstract: A heat exchanger positioned within an annular duct of a gas turbine engine is provided. The heat exchanger extends substantially continuously along the circumferential direction and defining a heat exchanger height equal to at least 10% of a duct height. An effective transmission loss (ETL) for the heat exchanger positioned within the annular duct is between 5 decibels and 1 decibels for an operating condition of the gas turbine engine. The heat exchanger includes a heat transfer section defining an acoustic length (Li), and wherein an Operational Acoustic Reduction Ratio (OARR) is greater than or equal to 0.75 to achieve the ETL at the operating condition.

Abstract: A heat exchanger positioned within an annular duct of a gas turbine engine is provided. The heat exchanger extends substantially continuously along the circumferential direction and defining a heat exchanger height equal to at least 10% of a duct height. An effective transmission loss (ETL) for the heat exchanger positioned within the annular duct is between 5 decibels and 1 decibels for an operating condition of the gas turbine engine. The heat exchanger includes a heat transfer section defining an acoustic length (Li), and wherein an Operational Acoustic Reduction Ratio (OARR) is greater than or equal to 0.75 to achieve the ETL at the operating condition.

Abstract: A heat exchanger positioned within an annular duct of a gas turbine engine is provided. The heat exchanger extends substantially continuously along the circumferential direction and defining a heat exchanger height equal to at least 10% of a duct height. An effective transmission loss (ETL) for the heat exchanger positioned within the annular duct is between 5 decibels and 1 decibels for an operating condition of the gas turbine engine. The heat exchanger includes a heat transfer section defining an acoustic length (Li), and wherein an Operational Acoustic Reduction Ratio (OARR) is greater than or equal to 0.75 to achieve the ETL at the operating condition.

Abstract: A heat exchanger positioned within an annular duct of a gas turbine engine is provided. The heat exchanger extends substantially continuously along the circumferential direction and defining a heat exchanger height equal to at least 10% of a duct height. An effective transmission loss (ETL) for the heat exchanger positioned within the annular duct is between 5 decibels and 1 decibels for an operating condition of the gas turbine engine. The heat exchanger includes a heat transfer section defining an acoustic length (Li), and wherein an Operational Acoustic Reduction Ratio (OARR) is greater than or equal to 0.75 to achieve the ETL at the operating condition.

Abstract: An inlet duct for a nacelle of a ducted fan engine includes an inlet portion having an inlet lip and a hardwall portion, a highlight plane defined at an upstream end of the inlet portion, and an acoustic liner downstream of the inlet portion, a hardwall-acoustic liner interface defined at an interface of the hardwall portion and the acoustic liner. The inlet portion and the acoustic liner are coupled at an inlet-acoustic liner interface extending circumferentially about an inner circumferential surface of the inlet duct. The inlet lip varies circumferentially and axially with respect to the highlight plane and the inlet centerline axis, and includes a plurality of inlet lip crests arranged along the highlight plane, and a plurality of inlet lip troughs arranged downstream of the highlight plane. The hardwall-acoustic liner interface extends circumferentially about the inner circumferential surface and is arranged axially parallel to the highlight plane.

Abstract: An inlet duct for a nacelle of a ducted fan engine includes an inlet portion at an upstream end of the inlet duct, an acoustic liner arranged downstream of the inlet portion, and a fan section arranged downstream of the acoustic liner. The inlet portion and the acoustic liner are coupled together at an inlet-acoustic liner interface extending circumferentially about the inner surface of the inlet duct, and the acoustic liner and the fan section are coupled together at a fan section hardwall-acoustic liner interface extending circumferentially about the inner surface of the inlet duct. At least one of the acoustic liner, the inlet-acoustic liner interface, and the fan section hardwall-acoustic liner interface having a structure that circumferentially alters a magnitude and a phase of an acoustic wave reflection of the inlet duct to attenuate flutter bite of a fan.

Abstract: An acoustic core may include an array of resonant cells configured as a plurality of resonant cell groups. The resonant cell groups may include a plurality of resonant cells configured as a partitioned resonant cell that include a converging resonant cell and a diverging resonant cell. The converging resonant cell and the diverging resonant cell may be defined by a plurality of cell walls integrally formed with one another and a partition integrally formed with the plurality of cell walls. The partition may at least partially delimit the converging resonant cell from the diverging resonant cell. The converging resonant cell may define an upper resonant space delimited by the partition and a top face of the array of resonant cells. The diverging resonant cell may define a lower resonant space delimited by the partition and a bottom face of the array of resonant cells.

Abstract: A gas turbine engine comprises a fan, a core turbine engine coupled to the fan, a fan case housing the fan and the core turbine engine, a plurality of outlet guide vanes extending between the core turbine engine and the fan case, and an acoustic spacing. The fan comprises a plurality of fan blades that define a fan diameter and a BEAL. The fan case comprises an inlet and an inlet length between the inlet and the fan. The acoustic spacing comprises a distance between the fan and the plurality of outlet guide vanes, and in combination with the BEAL determines an acoustic spacing ratio of the gas turbine engine.

Abstract: A gas turbine engine comprises a fan, a core turbine engine coupled to the fan, a fan case housing the fan and the core turbine engine, a plurality of outlet guide vanes extending between the core turbine engine and the fan case, and an acoustic spacing. The fan comprises a plurality of fan blades that define a fan diameter and a BEAL. The fan case comprises an inlet and an inlet length between the inlet and the fan. The acoustic spacing comprises a distance between the fan and the plurality of outlet guide vanes, and in combination with the BEAL determines an acoustic spacing ratio of the gas turbine engine.

Abstract: An acoustic core may include an array of resonant cells configured as a plurality of resonant cell groups. The resonant cell groups may include a plurality of resonant cells configured as a partitioned resonant cell that include a converging resonant cell and a diverging resonant cell. The converging resonant cell and the diverging resonant cell may be defined by a plurality of cell walls integrally formed with one another and a partition integrally formed with the plurality of cell walls. The partition may at least partially delimit the converging resonant cell from the diverging resonant cell. The converging resonant cell may define an upper resonant space delimited by the partition and a top face of the array of resonant cells. The diverging resonant cell may define a lower resonant space delimited by the partition and a bottom face of the array of resonant cells.

Abstract: A gas turbine engine is provided, having a turbomachine and a rotor assembly driven by the turbomachine and operable at a first blade passing frequency (f1) greater than or equal to 2,500 hertz and less than or equal to 5,000 hertz during a high power operating condition; a heat exchanger positioned within an annular duct and extending substantially continuously along the circumferential direction, wherein an effective transmission loss (ETL) for the heat exchanger positioned within the annular duct is between 5 decibels and 1 decibels for a high power operating condition, and wherein the heat exchanger comprises a heat transfer section defining an acoustic length (Li), and wherein an Operational Acoustic Reduction Ratio (OARR) is greater than or equal to 0.75 to achieve the ETL at the high power operating condition, the OARR equal to: sin ? ? ( 2 × ? × f 1 a 1 × L i ) 2 wherein a1 is equal to 13,200 inches per second during the high power operating condition.

Abstract: An inlet duct for a nacelle of a ducted fan engine includes an inlet portion at an upstream end of the inlet duct, an acoustic liner arranged downstream of the inlet portion, and a fan section arranged downstream of the acoustic liner. The inlet portion and the acoustic liner are coupled together at an inlet-acoustic liner interface extending circumferentially about the inner surface of the inlet duct, and the acoustic liner and the fan section are coupled together at a fan section hardwall-acoustic liner interface extending circumferentially about the inner surface of the inlet duct. At least one of the acoustic liner, the inlet-acoustic liner interface, and the fan section hardwall-acoustic liner interface having a structure that circumferentially alters a magnitude and a phase of an acoustic wave reflection of the inlet duct to attenuate flutter bite of a fan.

Abstract: An aircraft engine includes a low pressure spool, a high pressure spool, and an alternative power source. The alternative power source is configured to add power to the high pressure spool. A controller is configured to determine a noise sensitive condition; and control, in response to determining the noise sensitive condition, the alternative power source to add power to the high pressure spool.

Abstract: A gas turbine engine is provided. The gas turbine engine includes a turbomachine having a compressor section, a combustion section, and a turbine section arranged in serial flow order and together defining a working gas flowpath, the turbomachine including an acoustic liner, the acoustic liner having: a flowpath wall exposed to the working gas flowpath, the flowpath wall defining an opening; and a duct wall extending from the flowpath wall defining at least in part an acoustic passage defining a volume, the acoustic passage operable to attenuate noise through the working gas flowpath during an operating condition of the gas turbine engine.

Abstract: A blended wing body aircraft includes a body section having an aerodynamic lifting surface. The body section includes an upper body and a lower body. The blended wing body aircraft also includes a plurality of blended wing sections further defining the body section. The blended wing body aircraft includes one or more grooves in the body section. The one or more grooves extend from the upper body towards the lower body. The blended wing body aircraft further includes one or more open-fan engines mounted at least partially within the one or more grooves. The one or more open-fan engines ingest a portion of a boundary layer of the blended wing body aircraft.

Abstract: An acoustic core includes an array of resonant cells. The array may include a plurality of coupled resonant cells respectively defining an antecedent resonant space and a subsequent resonant space, with at least one cell wall having one or more wall-apertures defining a pathway between the antecedent resonant space and the subsequent resonant space. The array may include a plurality of high-frequency resonant cells respectively defining a high-frequency resonant space and being matched with respective ones of the plurality of coupled resonant cells. A cross-sectional dimension of the one or more wall-apertures defining the pathway between the antecedent resonant space and the subsequent resonant space may be less than a cross-sectional dimension of the antecedent resonant space and/or a cross-sectional dimension of the subsequent resonant space.